1. Technical Field
The present invention relates to an electro-optical device, a light receiving device, and an electronic apparatus which are preferable for a display equipment or the like for performing control of display luminance.
2. Related Art
A liquid crystal panel is constructed by enclosing liquid crystal between two substrates such as a glass substrate, a quartz substrate or the like. An electrode is provided on each substrate and an image signal is supplied to the electrodes. Optical property of liquid crystal positioned between electrodes of each substrate changes in accordance with the image signal. That is, alignment of liquid crystal molecules is changed by applying a voltage to the liquid crystal positioned between electrodes of each substrate based on the image signal. Thereby transmittance of light in each pixel is changed in accordance with the image signal and image display in accordance with the image signal is performed.
In order to perform high luminance display in such a liquid crystal panel, a backlight is generally provided on the back side of the liquid crystal panel. As for such a backlight, a device in which uniformity of illumination is improved by using a light guide plate has also been developed. Display on a display region can be observed at sufficient luminance by illuminating the display region of the liquid crystal panel with the backlight.
Incidentally, viewability of display of the liquid crystal panel is varied in accordance with brightness of periphery. For example, as the brightness of surrounding light becomes brighter, good viewability can be obtained as the illumination of the display region is increased. On the contrary, when surrounding light is sufficiently dark, it is not necessary to illuminate the display area beyond necessity.
In JP-A-2003-78838 (hereinafter, referred to as Patent Document 1), a technique is disclosed in which surrounding light is detected and luminance of a backlight is controlled with the feedback information thereof in order to provide good viewability regardless of brightness of the periphery.
In the device in Patent Document 1, as for an optical sensor for detecting surrounding light (outside light), a discreet component is employed. Accordingly, the optical sensor needs to be implemented on a flexible print substrate, causing increased number of man-hour and cost.
Consequently, it is preferable that an optical sensor using a PIN type diode is formed on a substrate constituting a display panel such as a liquid crystal panel or the like. In this case, the PIN type diode is formed on the same layer as a semiconductor layer in a viewing area.
However, in the semiconductor layer in the viewing area, a gate electrode needs to be formed on the semiconductor layer in order to form a self aligned LDD structure. In order to prevent injecting an impurity into an intrinsic layer, a mask of conductive material (hereinafter, referred to as mask conductive layer) needs to be formed on the intrinsic layer and in the same layer as the gate electrode also in a PIN type diode formed region. When the mask conductive layer is remaining on the intrinsic layer, introduction of light to the intrinsic layer is restricted by the mask conductive layer, so that sufficient light sensitivity can not be obtained. Consequently, in the PIN type diode formed region, it is required to provide a process for removing the mask conductive layer, so that there is a problem in that the number of processes is increased.